The present invention relates to alpha particle absorbers, and more particularly to such absorbers for integrated circuits.
Integrated circuits are susceptible to alpha particles which may cause single event upsets or soft errors. As is well known, the alpha particles are commonly emitted by the metals, ceramics and other materials associated with a next level of assembly of an integrated circuit.
Alpha particle shields for integrated circuits are also known. See, for example, U.S. Pat. No. 6,043,429, METHOD OF MAKING FLIP CHIP PACKAGES, issued Mar. 28, 2000 by Blish, et al. and IBM TECHNICAL DISCLOSURE BULLETIN, 80A 05436, Alpha Particle Shield, pp. 1892-1893, October 1980, which are both incorporated in their entireties herein by reference. Organic shields for alpha particles are also known.
The present inventors believe that improvements in alpha particle shields are achievable. According to the present invention, an integrated circuit includes a semiconductor substrate, a plurality of last metal conductors disposed above the substrate, a bottom metallic layer disposed on the last metal conductors, a top metallic layer, and an alpha absorber disposed between the bottom and top metallic layers, the alpha absorber consisting essentially of a high-purity metal which is a good alpha-particle absorber and a very low alpha particle emitter.
In other words, a cap metallurgy which is typically used atop a final passivation of an integrated circuit is modified to include a high-alpha-absorption low-emission metallurgy.